A census, simply put, is people counting people, something that has been done for centuries. The oldest known census was conducted in Babylon about 5,000 years ago, and it counted not just people but livestock and crops.

Censuses are important for governments. They began in an era of empires, when rulers needed to know how many subjects they had, where they were and how much taxes they could collect from them. Today, censuses are still important for economic and social planning, which is why governments aim for comprehensive coverage whenever they conduct censuses. Unlike public opinion surveys and social science research, where a small sample of the population is used, a census aims to cover all households.

Let’s look at how our population has changed through the last four centuries.When the Spaniards occupied the Philippines, they did their censuses for purposes of extracting tribute and labor. The counts tended to be quite localized, and were often incomplete because there were many areas the Spaniards could not reach. They also tended to count only those who had been converted to Christianity; the infidels, well, didn’t count.

Based on different accounts of colonial administrators, the historian Anthony Reid, in his “Southeast Asia in the Age of Commerce, 1450-1680,” summarized estimates for the population in Southeast Asia during the time of early contact of the region with the West. His sources suggest the population of Luzon and the Visayas was about 668,000 around ...